Sand dunes migrate constantly unless the sand of which they are composed is prevented by vegetation from blowing away.
All over the world advancing sand dunes threaten roads, villages and crops. The rate at which dunes move varies, depending upon the velocity of the wind and the height of the dunes, the smaller dunes migrating faster. In France, on the Bay of Biscay, the sands have advanced at a rate of 15 to 105 ft per year, burying forests, farms, vineyards, churches and whole villages. Miles of towns and cities in central Asia are buried under dunes. In North Africa, moving dunes constantly threaten human communities and engulf previously fertile land. Dunes constantly encroach on the Suez canal.